A single-threaded executor which executes tasks on the same thread from which
they are spawned.

The crate provides:

CurrentThread is the main type of this crate. It executes tasks on the current thread.
The easiest way to start a new CurrentThread executor is to call
block_on_all with an initial task to seed the executor.
All tasks that are being managed by a CurrentThread executor are able to
spawn additional tasks by calling spawn.

Application authors will not use this crate directly. Instead, they will use the
tokio crate. Library authors should only depend on tokio-current-thread if they
are building a custom task executor.